Polyvinyl butyral resins belong to a class of well known synthetic plastic materials and are widely used in modern industries owing to their outstandingly unique characteristics including the possibility of their utilization both as a thermoplastic and as a thermosetting resin, solubility in various organic solvents, adhesiveness to metals, plastics and glassy materials and high mechanical strengths such as impact resistance, tensile strength and the like. Therefore, polyvinyl butyral resins are conventionally used, for example, as an adhesive for printed circuit boards, binder for ceramic materials and coating material as well as an interlayer for laminated shatter-prrof glass in the form of a film and so on.
Despite the versatile utilizability of polyvinyl butyral resins as mentioned above, however, there are some difficulties in the application thereof. For example, use of an organic solvent in various preparations mentioned above is accompanied by (1) a serious problem relative to the health administration in the working environment and complicated process due to the requirement for completely removing the organic solvent from the products by evaporation after application, (2) decrease in the solvent resistance of the shaped articles and (3) troubles due to the extremely high viscosity of a high-solid solution.
Furthermore, some problems still remain in the use of a polyvinyl butyral resin as an interlayer of laminated shatter-proof glass because films of the polyvinyl butyral resin must be shaped in advance followed by a sandwiching process of the film between two glass plates so that high-quality products can be prepared only with a complete quality control necessarily leading to an increase in the manufacturing costs. In addition, such a laminated glass is not always satisfactory in respect of the heat resistance.